Polyfluoroheterocyclic compounds. Part VIII. Nucleophilic substitution in heptafluoro-quinoline and -isoquinoline

Abstract

Nucleophilic substitution in heptafluoroquinoline and/or heptafluoroisoquinoline by various nucleophiles, e.g., sodium methoxide, ammonia, hydrazine, and lithium aluminium hydride is described. Monosubstitution and disubstitution in heptafluoroquinoline occurs at the 2- and 4-positions while in heptafluoroisoquinoline attack occurs first, specifically, at the 1-position and then at the 6-position. Oxidation of heptafluoroisoquinoline and the methoxy-derivatives gives tri- and di-fluoropyridine dicarboxylic acids which aid the analysis of the ¹⁹F n.m.r. spectra of the methoxy-derivatives and establish their structures. Analysis of the ¹⁹F n.m.r. spectra of the derivatives of heptafluoroquinoline also clearly distinguishes their structures. In both series, some very large coupling constants are observed which are assigned to peri F–F coupling. It is concluded that the major factor determining the orientation of nucleophilic substitution in these systems is the effect of the ring nitrogen on the relative stabilities of the transition states.